Biomedical subjects

F E Zink

Publications and source records attributed to F E Zink.

5 recordsLinked to original sources

PubMed1995

Blood flow velocity measurements: a comparison of 25 clinical ultrasonographic units.

A blood-mimicking flow phantom was used to evaluate the precision of velocity measurements acquired using 25 pulsed Doppler ultrasonographic units from four vendors. Measurements were made at four constant flow rates (12 to 50 cm/s peak velocity). The average standard deviation values of the peak and time-averaged velocities among all units and all flow rates were found to be 7 and 9% of the mean, respectively, while the corresponding values for a subgroup of 20 identical units were 5 and 8%. Considered in conjunction with other published data, this suggests that units should be calibrated to an institutional standard at the time of acceptance testing.

Blood Flow Velocity↗

PubMed1994

The measurement of radiation dose profiles for electron-beam computed tomography using film dosimetry.

The unique geometry of electron-beam CT (EBCT) scanners produces radiation dose profiles with widths which can be considerably different from the corresponding nominal scan width. Additionally, EBCT scanners produce both complex (multiple-slice) and narrow (3 mm) radiation profiles. This work describes the measurement of the axial dose distribution from EBCT within a scattering phantom using film dosimetry methods, which offer increased convenience and spatial resolution compared to thermoluminescent dosimetry (TLD) techniques. Therapy localization film was cut into 8 x 220 mm strips and placed within specially constructed light-tight holders for placement within the cavities of a CT Dose Index (CTDI) phantom. The film was calibrated using a conventional overhead x-ray tube with spectral characteristics matched to the EBCT scanner (130 kVp, 10 mm A1 HVL). The films were digitized at five samples per mm and calibrated dose profiles plotted as a function of z-axis position. Errors due to angle-of-incidence and beam hardening were estimated to be less than 5% and 10%, respectively. The integral exposure under film dose profiles agreed with ion-chamber measurements to within 15%. Exposures measured along the radiation profile differed from TLD measurements by an average of 5%. The film technique provided acceptable accuracy and convenience in comparison to conventional TLD methods, and allowed high spatial-resolution measurement of EBCT radiation dose profiles.

Electrons↗

PubMed1994

Radiation dosimetry for electron beam CT.

PURPOSE: To measure the radiation dose profile, multiple-scan average dose (MSAD), and computed tomography dose index (CTDI) for electron beam CT and to determine the accuracy of ionization-chamber and manufacturer estimates of patient dose. MATERIALS AND METHODS: High-resolution dose profiles along the longitudinal axis were acquired at several positions within the scan plane with use of radiographic film. The full-width-at-half-maximum values, peak radiation dose, CTDI, and MSAD were calculated from the digitized film profiles. CTDI was also measured with an ionization chamber. RESULTS: The full-width-half-maximum value of the radiation profiles were significantly wider than the nominal scan width for the 6-mm single-section and 8-mm multisection modes. In the single-section mode, the CTDI underestimated the MSAD by 15%-30%. The multisection radiation profile was nonuniform and asymmetric. CONCLUSION: Patient doses in electron beam CT are approximately 125% of the ionization-chamber CTDI measurements in the single-section mode. For the multisection mode, the average patient dose over the scan volume is approximately 70%-85% of the ionization-chamber CTDI measurements.

Humans↗

PubMed1994

Conventional chest radiography vs dual-energy computed radiography in the detection and characterization of pulmonary nodules.

OBJECTIVE: We evaluated a single-exposure, phosphor-plate, dual-energy imaging device that produces, in addition to conventional chest radiographs, both tissue- and bone-selective images. Our purpose was to determine whether dual-energy radiography was more accurate than routine chest radiography for detection and characterization of pulmonary nodules. SUBJECTS AND METHODS: Two hundred patients undergoing chest CT were asked to volunteer to have dual-energy and conventional chest radiographs obtained immediately before or after their CT scan. Radiographs from a subset of 50 of these patients with 116 CT-detected nodules and 10 patients with normal findings on CT scans of the chest were presented to the observers for the nodule detection study. Similarly, radiographs from a subset of 29 patients with 20 calcified and 20 uncalcified nodules were presented to five observers to determine nodule calcification. Dual-energy images were produced by filtering the X-ray tube output with a gadolinium sheet while using a multiple phosphor plate receptor. A dual-energy triad of images consisting of a conventional image, a tissue-selective image, and a bone-selective image were produced. The conventional chest radiographs and dual-energy image sets were presented to observers in random order. Data from a free response receiver operating curve and a receiver operating curve were generated for nodule detection and characterization, respectively. RESULTS: By using the dual-energy images, all five observers improved their ability to diagnose pulmonary nodules (p = .0005) and to characterize nodules as calcified (p = .005). CONCLUSION: By eliminating rib shadows with tissue-selective images and enhancing calcified structures with bone-selective images, dual-energy chest radiography improved the ability of all observers, regardless of expertise, to detect and characterize pulmonary nodules.

False Positive Reactions↗

PubMedDate not supplied

X-ray tubes.

The x-ray tube serves the function of creating x-ray photons from electric energy supplied by the x-ray generator. The process of creating the x-ray beam is very inefficient, with only 1% of the electric energy converted to x-ray photons and the remaining 99% converted to heat in the x-ray tube assembly. Thus, to produce sufficient x-ray output for diagnostic imaging, the x-ray tube must withstand and dissipate a substantial heat load, a requirement that affects the design and composition of the x-ray tube. The major x-ray tube components are the cathode and anode assemblies, the tube envelope, the rotor and stator (for rotating anode systems), and the tube housing. The design of the x-ray tube determines the basic characteristics of the x-ray beam such as focal spot size, x-ray field uniformity, and the x-ray energy spectrum. These x-ray beam characteristics are important because they affect radiologic parameters such as spatial resolution, image contrast, and patient dose.

Technology, Radiologic↗